An Australian apartment block was placed under strict lockdown with police posted outside, as authorities stepped up efforts to curb a fast growing coronavirus outbreak.

Police guarded both the front and rear exits of an apartment block in Sydney's Bondi neighbourhood, where nine people have tested positive for Covid-19, with movement in and out of the building restricted, AFP reports.

Sydney is currently in its third week of a partial lockdown as authorities try to stamp out the spread of the virus in the community.

Most residents of Australia's largest city are allowed to leave home for exercise, essential shopping, work or health reasons, but are encouraged to remain at home.